Multiplication
Remember to put a zero in the empty place. Multiplying by 10 H T U 4 5 X 1 When you multiply by 10, all the digits move one place to the left. 4 5 Remember to put a zero in the empty place. Remember: A quick way to multiply a whole number by 10 is to put a zero on the end. © 2006 Paul Howarth
Fill up the two empty places with two zeros. Multiplying by 100 Th H T U 4 5 X 1 When you multiply by 100, all the digits move two places to the left. 4 5 Fill up the two empty places with two zeros. Remember: A quick way to multiply a whole number by 100 is to put two zeros on the end. © 2006 Paul Howarth
Multiplying large numbers Look at this example: Th H T U 2 3 7 X 5 Step 1: Start with the units. 5 x 7 = 35. Put 5 in the units column and carry the 3 into the tens. 1 1 8 5 1 3 Step 2: Now the tens. 5 x 3 = 15. Add the 3 you carried to get 18. Put 8 in the tens column and carry the 1 into the hundreds. Step 3: Now the hundreds. 5 x 2 = 10. Add the 1 you carried to get 11. Write 1 in the hundreds column and 1 in the thousands. © 2006 Paul Howarth
Multiplying large numbers Now look at this example: TTh Th H T U 2 3 7 4 5 Step 1: Multiply 237 by 5 just like we did last time. Step 2: The 4 is in the tens column so has the value 40. x 1 1 1 8 3 5 To multiply by 40, we multiply by both 10 and 4. + 9 1 4 2 8 Put a zero in the units column to multiply by 10. 1 6 6 5 Now multiply by 4. 1 Step 3: Add to get your answer. © 2006 Paul Howarth
Multiplying large numbers TTh Th H T U 2 3 7 4 5 The two most common mistakes. x 1 1 1 8 3 5 1. Forgetting this zero. + 9 1 4 2 8 1 6 6 5 1 2. Getting the carrying figures muddled up – keep them separate. © 2006 Paul Howarth
Lattice method 2 3 7 4 5 Here is another way to multiply 237 x 45. We are multiplying a three digit number by a two digit number, so draw a table with 3 columns and two rows like this: Now put 237 across the top and 45 down the right hand side. 2 3 7 4 5 © 2006 Paul Howarth
Lattice method Now fill in the squares by multiplying. 2 x 4 = 8 (no tens and 8 units) 3 x 4 = 12 7 x 4 = 28 2 3 7 2 1 4 8 2 8 1 1 3 5 5 5 7 x 5 = 35 2 x 5 = 10 3 x 5 = 15 © 2006 Paul Howarth
Don’t forget the 1 you’re carrying! Lattice method Now add up following the diagonal lines: 2 3 7 2 1 4 8 2 8 1 1 3 5 5 5 1 1 1 6 6 5 Don’t forget the 1 you’re carrying! So 237 x 45 = 10665 © 2006 Paul Howarth